Ordinarily, an entire packet is transferred at once, occupying an interface for as long as it takes to transfer the packet. Lengthy packets can monopolize an interface for relatively long periods of time. This can delay other packets which share the interface, affecting their QoS. It also increases the amount of buffer required at the input to shared interfaces to smooth out bursts caused by lengthy packets.
Instead of transferring an entire lengthy packet at once, it is transferred in fixed length segments followed by a single final segment of any length, termed Long Packet Handling. This puts a small bound on the maximum period any one packet can occupy an interface, reducing the effect it has on the QoS of packets belonging to other connections. This also reduces store-and-forward requirements because the Aggregator can begin forwarding a packet as soon as it receives a segment instead of waiting until it receives the entire packet. This simple form of segmentation and reassembly requires only as many contexts as there are sources.